* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    font-family: Arial, Helvetica, sans-serif;
}
.container {
    width: 100%;
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    background-color: chocolate;
    transition: 0.8s;
}

.container .btn {
    padding: 15px;
    background-color: white;
    border: none;
    outline: none;
    color: black;
    font-size: 20px;
    width: 200px;
    border-radius: 6px;
    cursor: pointer;
}

.container .btn.clicked {
    color: white;
    background-color: black;
}